1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and more particularly, to a method of fabricating a semiconductor device by filling carbon nanotubes in a recess.
2. Description of the Related Art
A carbon nanotube (CNT) used in the art to which the present invention pertains has been discovered by chance during a process of synthesizing fullerene (C60), one of allotrope of carbon. In the carbon nanotube, a carbon atom is combined with three peripheral carbon atoms by hybrid orbital sp2 to form a hexagonal honeycomb pattern and a graphene structure with the hexagonal honeycomb patterns is folded in a cylindrical shape to thereby form the carbon nanotube.
The carbon nanotube is fabricated as a single-wall nanotube (SWNT) and a multi-wall nanotube (MWNT) according to synthesizing conditions, and can be grown in various forms according to synthesizing methods. Several methods have been proposed to synthesize the carbon nanotube, of which an arc discharge method and a laser ablation method allow the carbon nanotube with relatively high purity to synthesize at a laboratory level and a chemical vapor deposition (CVD) method of allowing a large amount of carbon nanotubes to synthesize is commonly used to be applied for a display and a nano device.
Each of the conventional methods will be described in detail.
The laser ablation method can synthesize only the SWNT, and it can obtain relatively high purity, compared to other methods. According to this method, a test sample obtained by mixing a transition metal and graphite powders at a predetermined ratio within a quartz tube of a melting furnace heated to a temperature of 1,200° C. is evaporated by using laser from outside, which is then moved to a cooler through argon, a buffer gas, and then collected.
The arc discharge method, the first introduced synthesizing method, is a fabrication method obtained by modifying an apparatus when the carbon nanotube was first discovered. In this method, carbon nanotubes are formed by discharging arc between two carbon bars. Herein, it is known that the largest amount of carbon nanotubes can be synthesized in an environment having a uniform pressure of 400 to 700 torr with helium gas and a uniform cooling speed.
The CVD is a method in which when a raw material gas comprising a desired material is injected into a reactor, it receives energy from heat or plasma to be decomposed. In this process, the desired material reaches a surface of a substrate to thereby form a film.
However, the conventional synthesizing methods have some problems with respect to their application in using the carbon nanotubes as follows.
The laser ablation method can provide only the SWNT and cannot control a SWNT having semiconductor characteristics and a SWNT having conductor characteristics. In addition, this method cannot synthesize a large amount of carbon nanotubes. Accordingly, this method is not suitable for commercializing carbon nanotube application products.
In case of the arc discharge method, since the carbon nanotubes are formed through an arc discharge between the two carbon bars, it cannot have high purity and can contain various impurities. Like the laser ablation method, this method also has a large structural difficulty in synthesizing a large amount of carbon nanotubes.
The CVD method allows a large amount of carbon nanotubes to synthesize with relatively high purity, and as shown in FIG. 1, carbon nanotubes can be formed at desired portions by patterning a transition metal, which is a metal catalyst. However, this method also has a problem that the carbon nanotubes are formed only in a vertical direction on the metal catalyst, and since the metal catalyst is requisite for formation of the carbon nanotubes, its application field is limited.
In addition, most of the synthesizing methods require a high temperature process (about 500° C. to 4000° C.). Accordingly, in order to selectively obtain carbon nanotubes, existent methods used in the semiconductor process are quite limited. Moreover, since most of the synthesizing methods cannot form the carbon nanotubes in a multi-layer configuration, their application is limited only to a planar structure.
Furthermore, since the carbon nanotubes synthesized in the directly patterned shape contain various impurities such as amorphous carbon and the metal catalyst, a purification process must be performed on the carbon nanotubes.
FIG. 1 is a cross-sectional view illustrating sequential processes of a conventional CVD method.
As shown in FIG. 1, the structure obtained by performing the processes of the conventional CVD method comprises a substrate 1, a metal catalyst 2, a mold 3, and carbon nanotubes 5.
Processes of forming the carbon nanotubes on the substrate 1 by using the conventional CVD method will now be described.
Reference numeral 100A indicates a step of forming the mold 3 in the processes of the CVD method. In this step, the metal catalyst 2 is mounted on an upper surface of the substrate 1 and then the patterned mold 3 is mounted on an upper surface of the metal catalyst 2. The mold 3 is a sort of a photosensitive material such as photoresist.
Reference numeral 100B indicates a step of patterning the mold 3 mounted on the metal catalyst 2. In this step, infrared rays are applied onto the upper surface of the formed mold 3 for a predetermined time. Accordingly, a portion of the metal catalyst 2 that is received the infrared rays, except for the portion on which the mold 3 is mounted, can be patterned through a photolithography process.
Reference numeral 100C indicates a step of forming carbon nanotubes 5 on the upper surface of the metal catalyst 2 that is patterned through a high temperature (about 500° C. to 4000° C.) synthesizing method.
As afore-mentioned, the processes of the conventional CVD method have the problem that the carbon nanotubes are formed only vertically on the metal catalyst 2 and the metal catalyst 2 is requisite, resulting in a limitation of its application field.